It has become the "official" portrait of Bonnie Prince Charlie, regarded by the Oxford Dictionary of National Biography as the best likeness of the Jacobite hero. But now, in an embarrassing climbdown, the National Galleries of Scotland has admitted that the painting – purchased by them for £22,000 – is not of Charles Edward Stuart at all. As a few dealers suspected, the portrait, by the French master Maurice-Quentin La Tour, depicts his brother Cardinal Henry...